It really depends what you're interested in accomplishing. If you want to DIY a self-hosted, custom classification solution then TensorFlow, Caffe, Torch7, etc

It really depends what you're interested in accomplishing. If you want to DIY a self-hosted, custom classification solution then TensorFlow, Caffe, Torch7, etc are your best bet. ClarifAI, Watson, Google Cloud, Imagga will classify images into defined buckets through their hosted API. Other cognitive services, like http://CloudSight.ai/ http://CloudSight.ai/, focus on providing a deeper understanding to the image (fine-grained object recognition or scene captioning) using a massive library (currently over 350M+ images) in order to accomplish the task, though we can also utilize custom libraries. Disclaimer: I'm the co-founder of CloudSight. We, of course, would also be happy to discuss a solution with you as well. You can contact us at: contact@cloudsightapi.com